The planar-graph package

Planar graphs are graphs that can be embedded onto a surface
(i.e. they can be drawn on that surface without any edges crossing).
As such, it is preferable to use a dedicated data structure for them
that has information about how to achieve this embedding rather than a
standard graph data structure.

(Please note however that this implementation has only been tested in
terms of the embedding being on the unit sphere or disc; whether it
works or not as-is on any other type of surface is unknown.)